Stuart will most likely be the scapegoat.
For myself, I'm going to say Briere. I just have that feeling when someone gets injured, he's going to be thrown into a top 6 position that he can't handle.
I actually think Briere is going to surprise people in a good way. He was one of Montreal's best players in the playoffs, and his production vs playing time is damn good.
If you read a lot of the reports about Briere, no one could understand why he was getting so little playing time.
Not that he should be a full time top 6 forward, but he is a premier clutch player, and Roy will give him opportunities that he didn't get in Montreal.
Edit... Now Mitchell has a tendency to make his line-mates pretty much disappear, so I do worry about McGinn and Briere playing with him at center ice, but we'll see...
I'd personally like a McGinn - Briere - Talbot 3rd line, and hate the idea of Mitchell at center beyond the 4th line for these reasons.